Beijing -LRB- CNN -RRB- -- At just after midnight on Saturday , in a bar down an old lane in Beijing , the band suddenly stops playing . Grabbing the microphone , the manager tells everyone to remain in the venue ; the police are outside threatening to escort to the nearest police station any foreigner not carrying valid documents . The atmosphere instantly sours .

This is just one of many incidents that have occurred in Beijing over the weekend following last week 's launch of a 100-day campaign to `` clean out '' non-Chinese living or working illegally in the city . Until the end of August , all foreigners are expected to always have on them a valid passport , visa and resident permit , as stipulated by an announcement on Peaceful Beijing , the official Beijing Public Security Bureau account on popular Chinese micro-blogging site Sina Weibo .

If not , they will face repercussions , which range from fines to police detention and deportation .

A number for a hotline locals can call to report suspicious foreigners was also included in the announcement . Since then , the police presence in the main expat and student areas of the city has noticeably increased , households and companies have been spot checked , and queues at local police stations to register residency are large .

Lin Song , media officer of the Exit-Entry Administration Department under the Beijing Municipal Public Security Bureau , was not available to immediately comment when asked about the crackdown . However , last week in an editorial in the Global Times , he remarked : `` Some foreigners do not know Chinese laws well , and they might feel strange being randomly questioned by the police , but it is necessary to improve their legal awareness and make sure they stick to Chinese regulations . ''

Beijing police announced on Thursday that the city 's friendly attitude toward foreigners has not changed . `` Beijing will stick to the policy of reform and opening up , and we sincerely welcome foreign friends to work and live in Beijing , '' a spokesman told the state-run Xinhua news agency , adding that foreigners ' legitimate rights will be protected.Â

But the crackdown has left a bitter taste in the mouths of many , not least those who have resided in the city for years and see it as home . Media worker Jacob Trent was pulled off his bike by the police on Saturday and demanded to produce his papers . `` I have been living here for a decade and yet I still get treated like -- and sometimes called -- a foreign barbarian , '' lamented the American , who speaks perfect Mandarin and is engaged to a Chinese girl .

Another longtime expat , David Park , was equally distressed . `` I have noticed a change in how I am treated . It has gone from curiosity to hostility , '' commented Park . The 27-year-old , an employee at a renewable energy firm , has been contemplating a move back to England . These events will make his decision easier , he said .

Park was not the only person expressing a desire to leave in the wake of tensions . Mia Bate , an African-American doing an internship , has no intention to renew her visa once it expires in September . `` I never used to notice people looking at me on the streets , '' she said . `` Now I do and it makes me feel really uncomfortable . ''

The campaign comes amid a heated online debate about the behavior of foreigners in China . The most noticeable example has been the uploading of a video onto the Chinese video sharing site Youku of a foreign man sexually assaulting a Chinese woman in Beijing . The video attracted more than 11 million views and 80,000 comments to date . Beijing police revealed the foreigner in the video to be a Briton on a tourist visa .

Police deny the incidents are related , but in the minds of both foreigners and Chinese they are . Prominent host on Chinese Central Television , Yang Rui , posted on Sina Weibo that Beijing must clean out its `` foreign trash '' to `` protect innocent girls . '' According to Yang , they must `` cut off the foreign snake heads . ''

Similar rhetoric has been voiced by locals offline . When Beijing resident Mandy Zhang 's mother caught wind of the video , she called her 26-year-old daughter and asked her not to visit places that foreigners frequent . For both mother and daughter , the visa crackdown might not be an ideal solution , but it is necessary .

`` Police can not tell who is good or not . Some foreign men come here with the wrong intentions , '' Zhang said , adding : `` We treat Westerners too well and this needs to change . ''

According to statistics provided by the city government , Beijing is home to about 120,000 foreigners . Most have arrived during the past decade , attracted by a booming economy and a visa policy that has been relatively relaxed . Crackdowns on this scale are very rare , with the last noticeable one being in the lead up to the 2008 Beijing Olympics .

Lars Laaman , a professor of Chinese history at London 's SOAS , who has lived in the capital on and off since the 1980s , says these incidents only occur when the government is feeling uneasy , '' he commented , alluding to events that have gripped the nation over the past few months such as the dramatic fall from power of Chongqing party chief Bo Xilai .

Whatever the cause , as China 's economy continues to grow , its foreign population will likely rise too . Finding a workable solution to the visa situation will become increasingly important .

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New regulations demand all foreigners carry a valid passport , visa and resident permit

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Locals can also call a number for a hotline to report `` suspicious foreigners ''

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Campaign comes amid a heated online debate about poor behavior of foreigners in China

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Some expat residents in China report increasing hostility towards them